U.S. patent application number 15/250005 was filed with the patent office on 2017-03-23 for semiconductor device and method of manufacturing semiconductor device.
This patent application is currently assigned to FUJI ELECTRIC CO., LTD.. The applicant listed for this patent is FUJI ELECTRIC CO., LTD.. Invention is credited to Yuichi HARADA, Yasuyuki HOSHI, Takashi SHIIGI.
Application Number | 20170084699 15/250005 |
Document ID | / |
Family ID | 58283296 |
Filed Date | 2017-03-23 |
United States Patent
Application |
20170084699 |
Kind Code |
A1 |
HOSHI; Yasuyuki ; et
al. |
March 23, 2017 |
SEMICONDUCTOR DEVICE AND METHOD OF MANUFACTURING SEMICONDUCTOR
DEVICE
Abstract
A semiconductor device, including a substrate, and a deposit
layer and a semiconductor layer formed sequentially on the
substrate. The semiconductor layer has selectively disposed therein
a first region, a second region and a contact region. A gate
electrode is disposed on the first region and the semiconductor
layer via a gate insulating film. A source electrode is formed in
contact with the contact region and the second region. A drain
electrode is disposed on the back surface of the substrate. The
source electrode has a first titanium (Ti) film, and a titanium
nitride (TiN) film, a second Ti film, and a metal film containing
aluminum (Al) sequentially formed on the first Ti film. The source
electrode may further include another TiN film, on which the first
Ti film is formed.
Inventors: |
HOSHI; Yasuyuki;
(Matsumoto-city, JP) ; HARADA; Yuichi;
(Matsumoto-city, JP) ; SHIIGI; Takashi;
(Matsumoto-city, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJI ELECTRIC CO., LTD. |
Kawasaki-shi |
|
JP |
|
|
Assignee: |
FUJI ELECTRIC CO., LTD.
Kawasaki-shi
JP
|
Family ID: |
58283296 |
Appl. No.: |
15/250005 |
Filed: |
August 29, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 29/1608 20130101;
H01L 29/66068 20130101; H01L 23/564 20130101; H01L 29/7802
20130101; H01L 29/45 20130101; H01L 29/41741 20130101 |
International
Class: |
H01L 29/16 20060101
H01L029/16; H01L 29/78 20060101 H01L029/78; H01L 29/66 20060101
H01L029/66; H01L 23/29 20060101 H01L023/29; H01L 23/31 20060101
H01L023/31; H01L 27/088 20060101 H01L027/088; H01L 29/45 20060101
H01L029/45 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 17, 2015 |
JP |
2015-184248 |
Claims
1. A semiconductor device, comprising: a substrate formed of a
wide-band-gap semiconductor material that has a band gap greater
than that of silicon, the substrate having a front surface and a
back surface; a deposit layer formed of the wide-band-gap
semiconductor material and having an impurity concentration lower
than that of the substrate, the deposit layer having a first side
and a second side opposite to the first side, and being deposited
on the front surface of the substrate that is located on the second
side; a semiconductor region selectively disposed in the deposit
layer on the first side thereof; a semiconductor layer formed of
the wide-band-gap semiconductor material, disposed on a surface of
the deposit layer on the first side and a surface of the
semiconductor region formed in the deposit layer, the semiconductor
layer having selectively disposed therein a first region, a second
region and a contact region; a gate electrode disposed, via a gate
insulating film, on the semiconductor layer and the first region;
an interlayer insulating film covering the gate electrode; a source
electrode in contact with the contact region and the second region;
a drain electrode disposed on the back surface of the substrate; a
plating film selectively disposed on the source electrode; and a
pin electrode in contact with the plating film, wherein the
substrate, the deposit layer, and the first and second regions
formed in the semiconductor layer are of a first conductivity type,
the semiconductor region, the semiconductor layer and the contact
region formed therein are of a second conductivity type, and the
source electrode has a first titanium (Ti) film, and a titanium
nitride (TiN) film, a second Ti film, and a metal film containing
aluminum (Al) sequentially formed on the first Ti film.
2. The semiconductor device according to claim 1, wherein the
source electrode further includes another TiN film, on which the
first Ti film is formed.
3. The semiconductor device according to claim 1, wherein the metal
film containing Al is any one of an Al-silicon (Si) film, an Al--Cu
(Copper) film, and an Al--Si--Cu film.
4. The semiconductor device according claim 1, further comprising:
a protective film selectively disposed on the source electrode; and
a second protective film covering a junction of the plating film
and the protective film, wherein the second protective film is a
polyamide film.
5. The semiconductor device according claim 1, wherein the first
region is formed on the semiconductor region.
6. The semiconductor device according claim 1, wherein the pin
electrode is soldered to the plating film.
7. A method of manufacturing a semiconductor device, comprising:
providing a substrate of a first conductivity type, formed of a
wide-band-gap semiconductor material that has a band gap greater
than that of silicon; forming, on a front surface of the substrate,
a deposit layer made of the wide-band-gap semiconductor material,
the deposit layer being of the first conductivity type and having
an impurity concentration lower than that of the substrate;
selectively forming, in the deposit layer, a semiconductor region
of a second conductivity type; forming, on a surface of the deposit
layer, a semiconductor layer of the second conductivity formed of
the wide-band-gap semiconductor material; selectively forming a
first region of the first conductivity type in the semiconductor
layer; selectively forming a second region of the first
conductivity type in the semiconductor layer; selectively forming a
contact region of the second conductivity type in the semiconductor
layer; forming a gate electrode on the semiconductor layer and the
first region via a gate insulating film; forming an interlayer
insulating film to cover the gate electrode; forming a source
electrode to contact the contact region and the second region,
including forming a first titanium (Ti) film, and forming a
titanium nitride (TiN) film, a second Ti film, and a metal film
containing aluminum (Al) sequentially on the first Ti film; forming
a drain electrode on a back surface of the substrate; selectively
forming a plating film on the source electrode; and forming a pin
electrode in contact with the plating film.
8. The method of claim 7, wherein the first region is formed on the
semiconductor region.
9. The method of claim 7, wherein forming the pin electrode
includes soldering the pin electrode to the plating film.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. 2015-184248,
filed on Sep. 17, 2015, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The embodiments discussed herein relate to a semiconductor
device and a method of manufacturing a semiconductor device.
[0004] 2. Description of the Related Art
[0005] Conventionally, silicon (Si) is used as a constituent
material of a power semiconductor device that controls high voltage
and/or large current. There are several types of power
semiconductor devices such as bipolar transistors, insulated-gate
bipolar transistors (IGBTs), and metal oxide semiconductor field
effect transistors (MOSFETs). These devices are selectively used
according to intended purpose.
[0006] For example, bipolar transistors and IGBTs have high current
density compared to MOSFETs, and can be adapted for large current
but cannot be switched at high speed. In particular, the limit of
switching frequency is about several kHz for bipolar transistors
and about several tens of kHz for IGBTs. On the other hand, power
MOSFETs have low current density compared to bipolar transistors
and IGBTs, and are difficult to be adapted for large current but
can be switched at high speed up to about several MHz.
[0007] However, there has been a strong demand in the market for a
power semiconductor device achieving both large current and high
speed. Thus, IGBTs and power MOSFETs have been intensively
developed and improved, and the performance of power devices has
substantially reached the theoretical limit determined by the
material. In terms of power semiconductor devices, semiconductor
materials replacing silicon have been investigated and silicon
carbide (SiC) has been focused on as a semiconductor material
enabling production (manufacture) of a next-generation power
semiconductor device with low on voltage, high-speed
characteristics, and high-temperature characteristics (see, for
example, K. Shenai, et al, "Optimum Semiconductors for High-Power
Electronics", IEEE Transactions on Electron Devices, September
1989, Vol. 36, No. 9, pages 1811-1823).
[0008] Silicon carbide is chemically very stable semiconductor
material, has a wide band gap of 3 eV, and can be used very stably
as a semiconductor even at high temperatures. Silicon carbide has a
critical electric field strength that is ten times that of silicon
or greater, and thus is expected to be a semiconductor material
that can sufficiently reduce on-resistance. These merits of silicon
carbide are common to other wide band gap semiconductors with a
band gap greater than silicon, such as gallium nitride (GaN). Thus,
a high-voltage semiconductor device can be achieved by using a wide
band gap semiconductor (see, for example, B. Jayant Baliga,
"Silicon Carbide Power Devices", U.S.A, World Scientific Publishing
Co., Mar. 30, 2006, page 61).
[0009] Such a high-voltage semiconductor device using silicon
carbide has a reduced loss; however, a carrier frequency that is
ten times that of a conventional semiconductor device using silicon
or greater is applied to the high-voltage semiconductor device when
being used in an inverter. When a semiconductor device is used for
high frequency applications, the temperature of generated heat
emitted to the chip increases and affects the reliability of the
semiconductor device. In particular, bonding wires are connected to
front surface electrodes on a front surface side of a substrate, as
a wiring member that carries out the voltage of the front surface
electrodes. When the semiconductor device is used at high
temperatures, the adhesion of the front surface electrodes and the
bonding wires drops, thereby affecting the reliability.
[0010] Use of a planar conductor member other than the wire bonding
has been proposed as another wiring member that carries out the
voltage of the front surface electrodes (see, for example, Japanese
Patent Application Laid-Open Publication No. 2014-99444).
[0011] A conventional silicon carbide semiconductor device in which
pin electrodes are connected to the front surface electrodes with
solder has also been proposed. FIG. 3 is a cross-sectional view
depicting a structure of a conventional silicon carbide
semiconductor device. An n-type silicon carbide epitaxial layer 2
is deposited on a surface of an n.sup.+-type silicon carbide
substrate 1, and p.sup.+ -type regions 10 are disposed on the
surface of the n-type silicon carbide epitaxial layer 2. The p-type
silicon carbide epitaxial layer 11 is disposed on the surface of
the p.sup.+-type regions 10. N-type well regions 12 are disposed in
the p-type silicon carbide epitaxial layer 11 and on portions of
the n-type silicon carbide epitaxial layer 2 where no p.sup.+-type
region 10 is disposed. N.sup.+-type source regions 4 and
p.sup.++-type contact regions 5 are disposed on the surface of the
p-type silicon carbide epitaxial layer 11.
[0012] Gate electrodes 7 are disposed, via a gate insulating film
6, on the surface of the p-type silicon carbide epitaxial layer 11,
at portions between the n.sup.+-type source regions 4 and the
n-type well regions 12. As an interlayer insulating film 13, a
phosphorus silicate glass (PSG) film 14 is selectively disposed on
the gate electrodes 7. Source electrodes 8 are disposed on the
surfaces of the n.sup.+-type source regions 4 and the p.sup.++-type
contact regions 5. The source electrodes 8 have, for example, a
two-layer structure of a first Ti film 21 and an Al--Si film 24. A
protective film 15 is selectively disposed on the source electrodes
8, while plating films 16 are disposed on portions where no
protective film 15 is disposed.
[0013] Second protective films 17 are disposed so as to cover
junctions of the plating films 16 and the protective film 15.
Solder 19 is disposed on the plating films 16 so as to connect the
plating films 16 to pin electrodes 18 coupled to an external
signal. A drain electrode 9 is disposed on a back surface side of
the n.sup.+-type silicon carbide substrate 1.
[0014] In the MOSFET having the structure depicted in FIG. 3, when
a voltage lower than or equal to the gate threshold is applied to
the gate electrodes 7 while a positive voltage being applied to the
drain electrode 9 with respect to the source electrodes 8, the p-n
junction of the p-type silicon carbide epitaxial layer 11 and the
n-type well regions 12 is reverse-biased, the breakdown voltage of
the active region is not reached, and no current flows. On the
other hand, when a voltage higher than or equal to the gate
threshold is applied to the gate electrodes 7, current flows due to
an inversion layer formed on the surface of the p-type silicon
carbide epitaxial layer 11 underneath the gate electrodes 7. Thus,
MOSFET can be switched by the voltage applied to the gate
electrodes 7.
SUMMARY OF THE INVENTION
[0015] According to one aspect of the present invention, a
semiconductor device includes a wide-band-gap semiconductor
substrate of a first conductivity type which is formed of a
semiconductor having a band gap greater than that of silicon; a
wide-band-gap semiconductor deposit layer of the
first-conductivity-type, deposited on a front surface of the
wide-band-gap semiconductor substrate and having an impurity
concentration lower than that of the wide-band-gap semiconductor
substrate; a semiconductor region of a second conductivity type,
selectively disposed in a surface layer of the wide-band-gap
semiconductor deposit layer on an opposite side of the
wide-band-gap semiconductor substrate;
[0016] a wide-band-gap semiconductor layer of the second
conductivity type, formed of a semiconductor having a band gap
greater than that of silicon, and disposed on surfaces of the
wide-band-gap semiconductor deposit layer and the semiconductor
region; a first region of the first conductivity type, selectively
disposed in the wide-band-gap semiconductor layer so as to be on
the wide-band-gap semiconductor deposit layer; a second region of
the first conductivity type, selectively disposed in the
wide-band-gap semiconductor layer; a contact region of the second
conductivity type, selectively disposed in the wide-band-gap
semiconductor layer; a gate electrode disposed, via a gate
insulating film, on the second region and the first region; a
source electrode contacting the contact region and the second
region; an interlayer insulating film that covers the gate
electrode; a drain electrode that is disposed on a back surface of
the wide-band-gap semiconductor substrate; a plating film that is
selectively disposed on the source electrode; and a pin electrode
connected to the plating film via solder and carry out a signal to
an external destination. The source electrode has a structure in
which at least a Ti film, a TiN film, a Ti film, and a metal film
containing aluminum are sequentially disposed.
[0017] In the semiconductor device, the source electrode has a
structure in which a TiN film, a Ti film, a TiN film, a Ti film,
and a metal film containing aluminum are sequentially disposed.
[0018] In the semiconductor device, the metal film containing
aluminum is any one of an Al--Si film, an Al--Cu film, and an
Al--Si--Cu film.
[0019] The semiconductor device further includes a protective film
selectively disposed on the source electrode; and a second
protective film covering a junction of the plating film and the
protective film. The second protective film is a polyamide
film.
[0020] According to another aspect of the present invention, a
method of manufacturing a semiconductor device, includes forming on
a front surface of a wide-band-gap semiconductor substrate of a
first conductivity type which is formed of a semiconductor having a
band gap greater than that of silicon, a wide-band-gap
semiconductor deposit layer of the first conductivity type having
an impurity concentration lower than that of the wide-band-gap
semiconductor substrate; selectively forming a semiconductor region
of a second conductivity type in a surface layer of the
wide-band-gap semiconductor deposit layer; forming on a surface of
the wide-band-gap semiconductor deposit layer, a wide-band-gap
semiconductor layer of the second conductivity which is formed of a
semiconductor having a band gap greater than that of silicon;
selectively forming a first region of the first conductivity type
in the wide-band-gap semiconductor layer so as to be on the
wide-band-gap semiconductor deposit layer; selectively forming a
second region of the first conductivity type in the wide-band-gap
semiconductor layer; selectively forming a contact region of the
second conductivity type in the wide-band-gap semiconductor layer;
forming a gate electrode on the second region and the first region
via a gate insulating film; forming a source electrode so as to
contact the contact region and the second region; forming an
interlayer insulating film so as to cover the gate electrode;
forming a drain electrode on a back surface of the wide-band-gap
semiconductor substrate; selectively forming a plating film on the
source electrode; and forming a pin electrode so as to be connected
to the plating film via a solder and carry out a signal to an
external destination. The forming of the source electrode includes
sequentially forming a Ti film, a TiN film, a Ti film, a metal film
containing aluminum.
[0021] Objects, features, and advantages of the present invention
are specifically set forth in or will become apparent from the
following detailed description of the invention when read in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a cross-sectional view depicting the structure of
a silicon carbide semiconductor device according to a first
embodiment;
[0023] FIG. 2 is a cross-sectional view depicting the structure of
a silicon carbide semiconductor device according to a second
embodiment; and
[0024] FIG. 3 is a cross-sectional view depicting the structure of
a conventional silicon carbide semiconductor device.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Embodiments of a semiconductor device and a method of
manufacturing a semiconductor device according to the present
invention will be described in detail with reference to the
accompanying drawings. In the present description and accompanying
drawings, layers and regions prefixed with n or p mean that
majority carriers are electrons or holes. Additionally, + or -
appended to n or p means that the impurity concentration is higher
or lower, respectively, than layers and regions without + or -. The
same n or p including + or - means similar impurity concentration,
and does not necessarily mean the same impurity concentration. In
the description of the embodiments below and the accompanying
drawings, identical constituent elements will be given the same
reference signs and will not be repeatedly described. Further, in
the present description, when Miller indices are described, "-"
means a bar added to an index immediately after the "-", and a
negative index is expressed by prefixing "-" to the index.
[0026] A semiconductor device according to the present invention is
formed with a wide band gap semiconductor. In a first embodiment, a
MOSFET is taken as an example to describe a silicon carbide
semiconductor device produced by using, for example, silicon
carbide (SiC) as a wide band gap semiconductor. FIG. 1 is a
cross-sectional view depicting a structure of the silicon carbide
semiconductor device according to the first embodiment. FIG. 1
depicts the state of an active region.
[0027] As depicted in FIG. 1, in the silicon carbide semiconductor
device according to the first embodiment, an n-type silicon carbide
epitaxial layer (wide-band-gap semiconductor deposit layer of a
first conductivity type) 2 is deposited on a first principal
surface (front surface) of an n.sup.+-type silicon carbide
substrate (wide-band-gap semiconductor substrate of the first
conductivity type) 1.
[0028] The n.sup.+-type silicon carbide substrate 1 is, for
example, a monocrystalline silicon carbide substrate into which
nitrogen (N) is doped. The n-type silicon carbide epitaxial layer 2
is a low-concentration n-type drift layer into which, for example,
nitrogen is doped at the impurity concentration lower than that of
the n.sup.+-type silicon carbide substrate 1. In the following
description, the n.sup.+-type silicon carbide substrate 1 and the
n-type silicon carbide epitaxial layer 2 are collectively called a
silicon carbide semiconductor base.
[0029] MOS gate (metal oxide semiconductor insulated gate)
structures (device structures) are formed on a front surface side
of the silicon carbide semiconductor base. In particular,
p.sup.+-type regions (semiconductor region of a second conductivity
type) 10 functioning as p-base layers are selectively disposed on a
surface layer of the n-type silicon carbide epitaxial layer 2 on
the opposite side of the n.sup.+-type silicon carbide substrate 1
(i.e., on the front surface side of the silicon carbide
semiconductor base).
[0030] A p-type silicon carbide epitaxial layer 11 (wide-band-gap
semiconductor layer of the second conductivity type) is deposited
on the surfaces of the n-type silicon carbide epitaxial layer 2 and
the p.sup.+-type regions 10. In the p-type silicon carbide
epitaxial layer 11, n-type well regions 12 (first region of the
first conductivity type) that penetrate the p-type silicon carbide
epitaxial layer 11 in a depth direction and reach the n-type
silicon carbide epitaxial layer 2 are disposed at portions above
the n-type silicon carbide epitaxial layer 2. The n-type well
regions 12 and the n-type silicon carbide epitaxial layer 2 form a
drift region.
[0031] In the p-type silicon carbide epitaxial layer 11 and apart
from the n-type well regions 12, n.sup.+-type source regions 4
(second region of the first conductivity type) are selectively
disposed at portions facing the p.sup.+-type regions 10 in the
depth direction. P.sup.++-type contact regions 5
(second-conductivity-type region) having an impurity concentration
higher than that of the p-type silicon carbide epitaxial layer 11
are selectively disposed between the n.sup.+-type source regions 4
in the p-type silicon carbide epitaxial layer 11.
[0032] Gate electrodes 7 are disposed, via a gate insulating film
6, on the surfaces of portions between the n.sup.+-type source
regions 4 and the n-type well regions 12 of the p-type silicon
carbide epitaxial layer 11. The gate electrodes 7 may be disposed
on the surfaces of the n-type well regions 12 via the gate
insulating film 6.
[0033] An interlayer insulating film 13 is disposed on the front
surface side of the silicon carbide semiconductor base so as to
cover the gate electrodes 7. A boron phosphorus silicate glass
(BPSG) film 100 is deposited as the interlayer insulating film
13.
[0034] Source electrodes 8 are disposed contacting and electrically
connected to the n.sup.+-type source regions 4 and the
p.sup.++-type contact regions 5 via contact holes of the interlayer
insulating film 13.
[0035] In the source electrodes 8, a first Ti (titanium) film 21, a
second TiN (titanium nitride) film 22, a second Ti film 23, and an
Al--Si film 24 are deposited in this order. The Al--Si film 24 is,
for example, an aluminum film including silicon at 1%.
[0036] The first Ti film 21 absorbs and blocks hydrogen (H)
atoms/ions entering from the outside or generated in the Al--Si
film 24, and thereby prevents the hydrogen atoms/ions from reaching
the interlayer insulating film 13 of the layer below. Thus, the
first Ti film 21 is made relatively thick. Hydrogen atoms/ions
(hereinafter, "hydrogen ions") are particles including hydrogen
atoms as a smallest constituent unit, i.e., hydrogen atoms,
hydrogen ions, and hydrogen molecules. The second TiN film 22
prevents the first Ti film 21 from disappearing due to alloying
with the Al--Si film 24. The second Ti film 23 improves adhesion
with the Al--Si film 24.
[0037] The Al--Si film 24 may be an Al--Si--Cu film or an Al--Cu
film. The Al--Si--Cu film is an aluminum film including silicon and
copper at several % or less. The Al--Cu film is an aluminum film
including copper at several % or less. Silicon or copper included
in the aluminum film may suppress corrosion of the aluminum film.
The aluminum film including silicon is hard, and thus contributes
mitigate stress.
[0038] A drain electrode 9 is disposed on the back surface of the
silicon carbide semiconductor base. A protective film 15 is
selectively disposed on the source electrodes 8, and plating films
16 are disposed on the source electrodes 8 where no protective film
15 is disposed. The protective film 15 protects the front surface
of the semiconductor device. The protective film 15 also prevents
the plating of the plating films 16 from flowing to the outside,
when the plating films 16 are formed. The protective film 15 also
protects an edge termination structure (not depicted) enclosing the
active region. The active region is a region where current flows
when the semiconductor device is in on-state. The edge termination
structure is a region that is disposed so as to enclose the active
region, relaxes the electric field of the drift layer on the front
surface side of the substrate, and prevents the breakdown
voltage.
[0039] Second protective films 17 are disposed so as to selectively
cover junctions of the plating films 16 and the protective film 15.
The second protective films 17 cover gaps between the plating films
16 and the protective film 15, and prevent solder 19, for example,
from entering the side of the base. The second protective films 17
function as masks when the solder 19 is disposed. The second
protective films 17 may cover the entire surface of the protective
film 15. Pin electrodes 18 connected to the plating films 16 via
the solder 19 are disposed as a wiring member that carries out the
voltage of the source electrodes 8 to an external destination. The
pin electrodes 18 have a pin shape, and are connected to the source
electrodes 8 to be perpendicular thereto.
[0040] For example, a 1200V-class MOSFET is taken as an example to
describe a method of manufacturing a silicon carbide semiconductor
device according to the embodiment. The n.sup.+-type silicon
carbide substrate 1 into which nitrogen is doped at an impurity
concentration of about 2.times.10.sup.19cm.sup.-3, for example, is
prepared. A principal surface of the n.sup.+-type silicon carbide
substrate 1 may be, for example, a (000-1) surface having an off
angle of about 4 degrees in the <11-20> direction.
[0041] The n-type silicon carbide epitaxial layer 2 into which
nitrogen is doped at an impurity concentration of
1.0.times.10.sup.16cm.sup.-3 is epitaxial-grown on the (000-1)
surface of the n.sup.+-type silicon carbide substrate 1, so as to
have a thickness of 10 .mu.m.
[0042] A mask having predetermined openings is formed with, for
example, resist by photolithography on the surface of the n-type
silicon carbide epitaxial layer 2. Using this resist mask as a
mask, a p-type impurity such as aluminum atoms is ion-implanted by
ion implantation, thereby forming the p.sup.+-type regions 10 on a
part of the surface region of the n-type silicon carbide epitaxial
layer 2. The mask used in the ion implantation for forming the
p.sup.+-type regions 10 is removed.
[0043] The p-type silicon carbide epitaxial layer 11 is
epitaxial-grown on the surface of the n-type silicon carbide
epitaxial layer 2, so as to have a thickness of 0.5 .mu.m, for
example. The p-type silicon carbide epitaxial layer 11 may be
epitaxial-grown so as to have an impurity concentration of
2.0.times.10.sup.16cm.sup.-3.
[0044] A mask having predetermined openings is formed with, for
example, resist by photolithography on the surface of the p-type
silicon carbide epitaxial layer 11. Using the resist mask as a
mask, n-type impurity such as nitrogen is ion-implanted by ion
implantation, thereby forming the n.sup.+-type source regions 4 on
a part of the surface region of the p-type silicon carbide
epitaxial layer 11. The mask used in the ion implantation for
forming the n.sup.+-type source regions 4 is removed.
[0045] A mask having predetermined openings is formed with, for
example, resist by photolithography on the surface of the p-type
silicon carbide epitaxial layer 11. Using this resist mask as a
mask, p-type impurity such as aluminum is ion-implanted by ion
implantation, thereby forming the p.sup.++-type contact regions 5
on a part of the surface region of the p-type silicon carbide
epitaxial layer 11. The mask used in the ion implantation for
forming the p.sup.++-type contact regions 5 is removed.
[0046] A mask having predetermined openings is formed with, for
example, resist by photolithography on the surface of the p-type
silicon carbide epitaxial layer 11. Using this resist mask as a
mask, n-type impurity such as nitrogen is ion-implanted by ion
implantation, thereby forming the n-type well regions 12 on a part
of the surface region of the p-type silicon carbide epitaxial layer
11. The mask used in the ion implantation for forming the n-type
well regions 12 is removed.
[0047] An anneal process is performed for activating the
n.sup.+-type source regions 4, the p.sup.++-type contact regions 5,
and the n-type well regions 12. The temperature and the time of the
anneal process may be 1620 degrees C. and 2 minutes,
respectively.
[0048] The n.sup.+-type source regions 4, the p.sup.++-type contact
regions 5, and the n-type well regions 12 may be formed in a
different order.
[0049] The front surface side of the silicon carbide semiconductor
base is subjected to thermal oxidation, and the gate insulating
film 6 having a thickness of 100 nm is formed. The thermal
oxidation may be performed in a mixed atmosphere of oxygen
(O.sub.2) and hydrogen (H.sub.2) at the temperature of about 1000
degrees C. Thus, each of the regions formed on the surfaces of the
p-type silicon carbide epitaxial layer 11 and the n-type silicon
carbide epitaxial layer 2 is covered by the gate insulating film
6.
[0050] As the gate electrode 7, a polycrystalline silicon layer
into which phosphorus (P), for example, is doped is formed on the
gate insulating film 6. The polycrystalline silicon layer is
patterned and selectively removed so as to be left on portions
between the n.sup.+-type source regions 4 and the n-type well
regions 12 of the p-type silicon carbide epitaxial layer 11. The
polycrystalline silicon layer may be left on the n-type well
regions 12.
[0051] As the interlayer insulating film 13, the BPSG film 100 is
formed so as to cover the gate electrodes 7. For example, a film of
a boron phosphorus silicate glass (BPSG) having the thickness of
1.0 .mu.m is formed. A reflow process is performed for flattening
the BPSG film 100.
[0052] Contact holes are formed by pattering and selectively
removing the interlayer insulating film 13, thereby exposing the
n.sup.+-type source regions 4 and the p.sup.++-type contact regions
5.
[0053] A nickel film is formed by, for example, a sputtering
process on the front surface side of the silicon carbide
semiconductor base. Ohmic contacts with the silicon carbide
semiconductor portions (the n.sup.+-type source regions 4 and the
p.sup.++-type contact regions 5) are formed by reacting the silicon
carbide semiconductor portions and the nickel film by sintering
(anneal process), thereby forming a nickel silicide film.
[0054] The first Ti film 21, the second TiN film 22, the second Ti
film 23, and the Al--Si film 24 are formed as the source electrodes
8. For example, the first Ti film 21 is formed by a sputtering
process, and the second TiN film 22 is formed by a sputtering
process on a top portion of the first Ti film 21. The second Ti
film 23 is formed by a sputtering process on a top portion of the
second TiN film 22. The Al--Si film 24 is formed by a sputtering
process on a top portion of the second Ti film 23. Instead of the
Al--Si film 24, an Al--Si--Cu film or an Al--Cu film may be formed.
Here, "top portion" means upper portion when the direction from the
n.sup.+-type silicon carbide substrate 1 to the n-type silicon
carbide epitaxial layer 2 is assumed as the upward direction.
[0055] A nickel film, for example, is formed as the drain electrode
9 on a surface of the n.sup.+-type silicon carbide substrate 1 (the
back surface of the silicon carbide semiconductor base). An ohmic
contact of the n.sup.+-type silicon carbide substrate 1 and the
drain electrode 9 is formed by an anneal process at the temperature
of 970 degrees C., for example.
[0056] As the drain electrode 9, for example, films of titanium,
nickel (Ni), and gold (Au) are formed in this order on the surface
of the nickel film. The protective film 15 is selectively formed on
the source electrodes 8 on the front surface side of the silicon
carbide semiconductor base.
[0057] Using the protective film 15 as a mask, the plating films 16
are selectively formed on the source electrodes 8 where no
protective film 15 is formed. Thus, the plating films 16 are formed
on the source electrodes 8, without the plating flowing to the edge
termination structure. Using polymer resin including an imide, such
as polyimide film, the second protective films 17 are selectively
formed so as to cover junctions of the plating films 16 and the
protective film 15.
[0058] The solder 19 is disposed on the plating films 16 using the
protective film 15 and the second protective film 17 as a mask in
the soldering, and the pin electrodes 18 connected to the plating
films via the solders are formed. Thus, the MOSFET depicted in FIG.
1 is completed.
[0059] As described above, according to the first embodiment, the
second TiN film disposed between the first Ti film and the Al--Si
film in the source electrodes may suppress the first Ti film from
becoming thinner due to alloying of the first Ti film and the
Al--Si film, thereby suppressing penetration of hydrogen ions into
the interlayer insulating film by the first Ti film. Thus, the
threshold voltage of a semiconductor device in the low current
range may be prevented from varying. The second Ti film disposed
between the second TiN film and the Al--Si film may improve the
adhesion of the source electrodes.
[0060] FIG. 2 is a cross-sectional view depicting a structure of a
silicon carbide semiconductor device according to a second
embodiment. The semiconductor device according to the second
embodiment differs from that according to the first embodiment in
that the source electrodes 8 have a five-layer structure in which a
first TiN film 20 is further deposited between the silicon carbide
semiconductor base and the first Ti film 21.
[0061] In the source electrodes 8, the first TiN film 20, the first
Ti film 21, the second TiN film 22, the second Ti film 23, and the
Al--Si film 24 are deposited in this order. The Al--Si film 24 may
be an Al--Si--Cu film or an Al--Cu film.
[0062] The first TiN film 20 prevents nickel (Ni) from diffusing
into the interlayer insulating film 13 in the anneal process for
forming the nickel silicide film.
[0063] A method of manufacturing a semiconductor device according
to the second embodiment is described. The process of forming the
n-type silicon carbide epitaxial layer 2 to the process of forming
the contact holes are sequentially performed in a similar manner to
the first embodiment.
[0064] As the source electrode 8, the first TiN film 20 is formed
by a sputtering process, for example. The first TiN film 20 is
selectively removed, thereby exposing the n.sup.+-type source
regions 4 and the p.sup.++-type contact regions 5 at the contact
holes again. A nickel film (not depicted) that contacts the silicon
carbide semiconductor portions (the n.sup.+ source regions 4 and
the p.sup.++-type contact regions 5) exposed at the contact holes
is formed by a sputtering process, for example. A nickel silicide
film is formed by reacting the silicon carbide semiconductor
portions and the nickel film by an anneal process, thereby forming
ohmic contacts with the silicon carbide semiconductor portions. The
first TiN film 20 arranged between the interlayer insulating film
13 and the nickel film prevents nickel atoms of the nickel film
from diffusing into the interlayer insulating film 13. Portions
that are of the nickel film and on the first TiN film 20 may be
left or removed.
[0065] As the source electrodes 8, the first Ti film 21, the second
TiN film 22, the second Ti film 23, and the Al--Si film 24 are
sequentially formed in a similar manner to the first
embodiment.
[0066] The process of forming the drain electrode 9 and the
subsequent processes are sequentially performed in a similar manner
to the first embodiment, thereby completing the MOSFET depicted in
FIG. 2.
[0067] As described above, the silicon carbide semiconductor device
and the manufacturing method thereof according to the second
embodiment may achieve the effect similar to that of the silicon
carbide semiconductor device and the manufacturing method thereof
according to the first embodiment.
[0068] According to the semiconductor device and the manufacturing
method thereof of the second embodiment, the first TiN film further
deposited between the silicon carbide semiconductor base and the
first Ti film in the source electrodes may prevent nickel atoms in
the nickel film from diffusing and entering the interlayer
insulating film during the anneal process for forming the ohmic
contacts. Thus, the threshold of the semiconductor device may be
prevented from varying.
[0069] The structure of a silicon carbide semiconductor device
according to a third embodiment is not depicted, since the
structure is similar to that according to the first embodiment. The
semiconductor device according to the third embodiment differs from
that according to the first embodiment in that the second
protective film 17 is a polyamide film. The polyamide film is a
synthetic polymer material including an amide in the molecule, and
has adhesion greater than the polyimide film.
[0070] Similar to the polyimide film, the polyamide film covers at
least triple-contact junctions where the plating film 16, the
protective film 15, and the source electrode 8 contact each other.
The polyamide film covering the triple-contact junctions improves
the adhesion with the plating films (or the source electrodes
exposed between the plating films and the protective film). The
second protective film 17 may cover the entire surface of the
protective film 15, thereby further improving the adhesion with the
plating films (or the source electrodes exposed between the plating
films and the protective film).
[0071] A method of manufacturing a silicon carbide semiconductor
device according to a third embodiment is described. The process of
forming the n-type silicon carbide epitaxial layer 2 to the process
of forming the plating films 16 are sequentially performed in a
similar manner to the first embodiment.
[0072] Using the polyamide film, the second protective films 17 are
selectively formed so as to cover junctions of the plating films 16
and the protective film 15.
[0073] The process of forming the pin electrodes 18 is performed in
a similar manner to the first embodiment, thereby completing the
silicon carbide semiconductor device according to the third
embodiment.
[0074] As described above, the silicon carbide semiconductor device
and the manufacturing method thereof according to the third
embodiment may achieve the effect similar to that of the silicon
carbide semiconductor device and the manufacturing method thereof
according to the first embodiment.
[0075] According to the semiconductor device and the manufacturing
method thereof according to the third embodiment, the polyamide
film used as the second protective films may improve the adhesion
with the plating films (or the source electrodes exposed between
the plating films and the first protective film), and may suppress
penetration of solder into the side of the silicon carbide
semiconductor base, thereby preventing degradation of the
characteristics of the semiconductor device and suppressing
degradation of the reliability.
[0076] In the third embodiment, the polyamide film is used as the
second protective films 17 of the silicon carbide semiconductor
device according to the first embodiment; However, the polyamide
film may be used as the second protective films 17 of the silicon
carbide semiconductor device according to the second embodiment. In
this case, the effect similar to that of the silicon carbide
semiconductor device and the manufacturing method thereof according
to the second embodiment may be obtained.
[0077] A MOSFET is taken as an example to describe the embodiments
of the present invention; however, not limited to this, the present
invention may be applied to various semiconductor devices having
various structures, for example, a MOS device such as IGBT, a
semiconductor device in which stress concentration occurs in the
device structure due to a step of the interlayer insulating film,
etc. An example where silicon carbide is used as the wide band gap
semiconductor is described in the embodiments described above;
however, a similar effect may be obtained by using a wide band gap
semiconductor other than silicon carbide, such as gallium nitride
(GaN). In the embodiments, the first conductivity type is an n-type
while the second conductivity type is a p-type; however, the
present invention may be implemented when the first conductivity
type is a p-type while the second conductivity type is an
n-type.
[0078] Further, in a conventional structure such as that depicted
in FIG. 3, since the source electrode 8 has a 2-layer structure of
the first Ti film 21 and the Al--Si film 24, the titanium and
aluminum form an alloy, whereby the first Ti film 21, which is a
hydrogen (H) adsorbing metal, disappears and the threshold voltage
may vary consequent to the negative impact of hydrogen ions from an
external source.
[0079] However, as described above, according to the present
invention, the second TiN film disposed between the first Ti film
and the Al--Si film in the source electrodes may suppress the first
Ti film from becoming thinner consequent to alloying of the first
Ti film and the Al--Si film, thereby suppress penetration of
hydrogen ions into the interlayer insulating film by the first Ti
film. Thus, the threshold of a semiconductor element in the low
current range may be prevented from varying. The second Ti film
disposed between the second TiN film and the Al--Si film may
improve the adhesion of the source electrodes.
[0080] The first TiN film further deposited between the silicon
carbide semiconductor base and the first Ti film in the source
electrodes may prevent nickel from diffusing and entering the
interlayer insulating film during the anneal process. Thus, the
threshold of the semiconductor device may be prevented from
varying.
[0081] The polyamide film used as the second protective films may
improve the adhesion with the plating films (or the source
electrodes exposed between the plating films and the protective
film), and may suppress penetration of solder into the side of the
silicon carbide semiconductor base, thereby preventing degradation
of the characteristics of the semiconductor device and suppressing
degradation of the reliability.
[0082] The semiconductor device and the method of manufacturing a
semiconductor device may suppress variation in characteristics, and
may provide a highly-reliable semiconductor device.
[0083] As described above, the semiconductor device according to
the present invention is useful for high-voltage semiconductor
devices used in power converting equipment such as converters and
inverters, and power supply devices such as those in various
industrial machines. In particular, the semiconductor device is
suitable for a silicon carbide semiconductor device that uses pin
electrodes as a wiring member to carry out the voltage of the front
surface electrodes.
[0084] Although the invention has been described with respect to a
specific embodiment for a complete and clear disclosure, the
appended claims are not to be thus limited but are to be construed
as embodying all modifications and alternative constructions that
may occur to one skilled in the art which fairly fall within the
basic teaching herein set forth.
* * * * *